An in-flight timeout (worker still pulling the OCI image) is not a
failed attempt, it's a delayed one. Incrementing Attempts let
genuinely-progressing slow installs (e.g. 30 GB CUDA images on Wi-Fi)
trip the reconciler's maxPendingBackendOpAttempts cap and dead-letter
the queue row while the worker was still legitimately working.
RecordPendingBackendOpInFlight now only updates LastError and NextRetryAt.
Also documents "running_on_worker" in the NodeOpStatus.Status enum
comment so Task 6 implementers see the full surface.
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>